算法Sedgewick第四版-第1章基础-018一解决不能声明泛型数组的两咱方法(强转或反射)

1.

 /******************************************************************************
  *  Compilation:  javac ResizingArrayStackWithReflection.java
  *  Execution:    java ResizingArrayStackWithReflection < input.txt
  *  Dependencies: StdIn.java StdOut.java
  *  Data files:   http://algs4.cs.princeton.edu/13stacks/tobe.txt
  *
  *  Stack implementation with a resizing array.
  *
  *  % more tobe.txt
  *  to be or not to - be - - that - - - is
  *
  *  % java ResizingArrayStackWithReflection < tobe.txt
  *  to be not that or be (2 left on stack)
  *
  *  Written by Bruno Lehouque.
  *
  ******************************************************************************/

 import java.lang.reflect.Array;
 import java.util.Iterator;
 import java.util.NoSuchElementException;

 /**
  * A LIFO Stack using a resizeable array.
  */
 public class ResizingArrayStackWithReflection<Item> implements Iterable<Item> {

     private Class<Item[]> itemArrayClass;
     private Item[] array;
     private int N = 0;

     public ResizingArrayStackWithReflection(Class<Item[]> itemArrayClass) {
         this.itemArrayClass = itemArrayClass;
         array = itemArrayClass.cast(Array.newInstance(itemArrayClass.getComponentType(), 1));
     }

     /**
      * Adds a non-{@code null} element on top of the Stack.
      *
      * @param item
      *      the element which is to be added to the Stack
      *
      * @throws IllegalArgumentException if {@code item} is {@code null}.
      */
     public void push(Item item) {
         if (item == null)
             throw new IllegalArgumentException("Cannot add null item.");
         if (N == array.length)
             resize(array.length * 2);
         array[N++] = item;
     }

     /**
      * Removes and returns the top element of the Stack.
      *
      * @return the top element of the Stack
      *
      * @throws NoSuchElementException if the Stack is empty
      */
     public Item pop() {
         if (isEmpty())
             throw new NoSuchElementException();
         Item item = array[--N];
         array[N] = null;
         if ((N > 0) && (N <= array.length / 4))
             resize(array.length / 2);
         return item;
     }

     /**
      * Returns, but doesn't remove, the top element of the Stack.
      *
      * @return the top element of the Stack
      *
      * @throws NoSuchElementException if the Stack is empty
      */
     public Item peek() {
         if (isEmpty())
             throw new NoSuchElementException();
         return array[N - 1];
     }

     /**
      * Returns {@code true} if the Stack is empty.
      *
      * @return {@code true} if the Stack is empty
      */
     public boolean isEmpty() {
         return N == 0;
     }

     /**
      * Returns the size of the Stack.
      *
      * @return the size of the Stack
      */
     public int size() {
         return N;
     }

     /**
      * Returns an iterator which iterates over the Stack from the top element
      * to the bottom element.
      *
      * @return an iterator which iterates over the Stack from the top element
      * to the bottom element
      */
     public Iterator<Item> iterator() {
         return new ReverseArrayIterator();
     }

     private void resize(int size) {
         Item[] newarray = itemArrayClass.cast(Array.newInstance(itemArrayClass.getComponentType(), size));
         for (int i = 0; i < N; i++)
             newarray[i] = array[i];
         array = newarray;
     }

     private class ReverseArrayIterator implements Iterator<Item> {

         private int i = N-1;

         @Override
         public boolean hasNext() {
             return i >= 0;
         }

         @Override
         public Item next() {
             if (!hasNext())
                 throw new NoSuchElementException();
             return array[i--];
         }

         @Override
         public void remove() {
             throw new UnsupportedOperationException("Not supported.");
         }

     }

     /**
      * Test client (copied from ResizingArrayStack).
      */
     public static void main(String[] args) {
         ResizingArrayStackWithReflection<String> s = new ResizingArrayStackWithReflection<String>(String[].class);
         while (!StdIn.isEmpty()) {
             String item = StdIn.readString();
             if (!item.equals("-")) s.push(item);
             else if (!s.isEmpty()) StdOut.print(s.pop() + " ");
         }
         StdOut.println("(" + s.size() + " left on stack)");
     }
 }

2.

 /******************************************************************************
  *  Compilation:  javac ResizingArrayStack.java
  *  Execution:    java ResizingArrayStack < input.txt
  *  Dependencies: StdIn.java StdOut.java
  *  Data files:   http://algs4.cs.princeton.edu/13stacks/tobe.txt
  *
  *  Stack implementation with a resizing array.
  *
  *  % more tobe.txt
  *  to be or not to - be - - that - - - is
  *
  *  % java ResizingArrayStack < tobe.txt
  *  to be not that or be (2 left on stack)
  *
  ******************************************************************************/

 import java.util.Iterator;
 import java.util.NoSuchElementException;

 /**
  *  The <tt>ResizingArrayStack</tt> class represents a last-in-first-out (LIFO) stack
  *  of generic items.
  *  It supports the usual <em>push</em> and <em>pop</em> operations, along with methods
  *  for peeking at the top item, testing if the stack is empty, and iterating through
  *  the items in LIFO order.
  *  <p>
  *  This implementation uses a resizing array, which double the underlying array
  *  when it is full and halves the underlying array when it is one-quarter full.
  *  The <em>push</em> and <em>pop</em> operations take constant amortized time.
  *  The <em>size</em>, <em>peek</em>, and <em>is-empty</em> operations takes
  *  constant time in the worst case.
  *  <p>
  *  For additional documentation,
  *  see <a href="http://algs4.cs.princeton.edu/13stacks">Section 1.3</a> of
  *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
  *
  *  @author Robert Sedgewick
  *  @author Kevin Wayne
  */
 public class ResizingArrayStack<Item> implements Iterable<Item> {
     private Item[] a;         // array of items
     private int N;            // number of elements on stack

     /**
      * Initializes an empty stack.
      */
     public ResizingArrayStack() {
         a = (Item[]) new Object[2];
         N = 0;
     }

     /**
      * Is this stack empty?
      * @return true if this stack is empty; false otherwise
      */
     public boolean isEmpty() {
         return N == 0;
     }

     /**
      * Returns the number of items in the stack.
      * @return the number of items in the stack
      */
     public int size() {
         return N;
     }

     // resize the underlying array holding the elements
     private void resize(int capacity) {
         assert capacity >= N;
         Item[] temp = (Item[]) new Object[capacity];
         for (int i = 0; i < N; i++) {
             temp[i] = a[i];
         }
         a = temp;
     }

     /**
      * Adds the item to this stack.
      * @param item the item to add
      */
     public void push(Item item) {
         if (N == a.length) resize(2*a.length);    // double size of array if necessary
         a[N++] = item;                            // add item
     }

     /**
      * Removes and returns the item most recently added to this stack.
      * @return the item most recently added
      * @throws java.util.NoSuchElementException if this stack is empty
      */
     public Item pop() {
         if (isEmpty()) throw new NoSuchElementException("Stack underflow");
         Item item = a[N-1];
         a[N-1] = null;                              // to avoid loitering
         N--;
         // shrink size of array if necessary
         if (N > 0 && N == a.length/4) resize(a.length/2);
         return item;
     }

     /**
      * Returns (but does not remove) the item most recently added to this stack.
      * @return the item most recently added to this stack
      * @throws java.util.NoSuchElementException if this stack is empty
      */
     public Item peek() {
         if (isEmpty()) throw new NoSuchElementException("Stack underflow");
         return a[N-1];
     }

     /**
      * Returns an iterator to this stack that iterates through the items in LIFO order.
      * @return an iterator to this stack that iterates through the items in LIFO order.
      */
     public Iterator<Item> iterator() {
         return new ReverseArrayIterator();
     }

     // an iterator, doesn't implement remove() since it's optional
     private class ReverseArrayIterator implements Iterator<Item> {
         private int i;

         public ReverseArrayIterator() {
             i = N-1;
         }

         public boolean hasNext() {
             return i >= 0;
         }

         public void remove() {
             throw new UnsupportedOperationException();
         }

         public Item next() {
             if (!hasNext()) throw new NoSuchElementException();
             return a[i--];
         }
     }

     /**
      * Unit tests the <tt>Stack</tt> data type.
      */
     public static void main(String[] args) {
         ResizingArrayStack<String> s = new ResizingArrayStack<String>();
         while (!StdIn.isEmpty()) {
             String item = StdIn.readString();
             if (!item.equals("-")) s.push(item);
             else if (!s.isEmpty()) StdOut.print(s.pop() + " ");
         }
         StdOut.println("(" + s.size() + " left on stack)");
     }
 }